1981 240D won't shift out of 2nd ! - PeachParts Mercedes-Benz Forum

wilburtual · #1 11-12-2013, 07:40 AM

my 1981 240D has been having transmission issues lately... for a couple of months it has been flaring pretty bad going from 2nd to 3rd, to get it to shift I'd let off on the pedal untill it shifts then ease it into 3rd...then also needed to east into 4th. i changed the fluid and filter hoping to help and it did help a little, didn't flare as much, but not great.

A couple days ago it started to not shift from 2nd at all. it will start in 1st and go to second, but then no matter what speed you try to get to, doesn't even try to go to third, no flaring just keeps on increasing RPM in second.

about a year ago, i had this same issue, stuck in second, and i found that the hard vacuum line that goes from the valve cover to the transmission was unplugged, once i plugged it back in, it started to shift as usual. so, this time i am hoping it is a vacuum issue again.. ??

I've check that all lines are plugged in and I ordered some replacements parts from pelicanparts. I replaced the little white plastic vacuum valve that is on the valve cover hoping it was that, since the little plunger flap was almost completely worn off. but, replaced it, no change. i also replaced all the rubber vacuum connections and junctions under the hood to try and find a leak. oh, and also changed the green vacuum damper dashpot thingy.

so,,, now I am wondering where to go next - does it still seem like a possible vacuum issue? how about the valve that is on the Injection pump, can that be a culprit? anything on the transmission itself? i read on another thread about a little cap on the transmission modulator can leak?

help!! thanks

Zacharias · #2 11-12-2013, 03:57 PM

To ensure meaningful replies, it would be best to confirm what model of transmission your car has. The number is stamped on the transmission body, the lip just above the pan, on the passenger side. It will likely be crusted over with grease and oil. If it's impractical for you to look, perhaps someone else will confirm....

I am going to go ahead and answer, as I am pretty sure it will be like the one in my wagon (which was originally in a 240d), a 722.117 or .118 -- in which case it's a vacuum-only controlled transmission (no lever to the transmission from the linkages).

To do what I suggest you will need a vacuum gauge and a vacuum tester, such as a Mityvac.

I suggest you proceed by:

1 - undo the main vacuum line running to the brake booster and measure the vacuum output of your vacuum pump with a vacuum gauge. Sorry I am not sure I remember the correct figure, I think it's anywhere between 18-22 hg? If it's low or jumping (gauge wavers really erratically), you need to replace the diaphragm in your injection pump.

2 - Apply vacuum through the vacuum line running down to the transmission to see if the vacuum modulator holds vacuum. If not, the cap may be leaking.

3 - if all seems good here, move to the whitish/yellow vacuum control valve bolted to the injection pump. This has a spring inside that acts on a bleed valve. Some of these get very tired and the spring needs to be retensioned. Link to DIY: http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1261744-transmission-flaring-clunking-vcv-diy.html (unfortunately some of these valves are not servicable, have a lock ring instead of the nut shown in the DIY... in this case you will have to get hold of a used valve that is adjustable).

I suspect your issue is lurking in one of these areas.

cooljjay · #3 11-12-2013, 08:02 PM

You have a kickdown switch behind the accelerator....if this gets stuck it can also cause your issue.... Does it work? To rule out that as a problem....simply unplug it....and see if there is a change...

wilburtual · #4 11-13-2013, 06:40 PM

thanks for the suggestions.
I have unplugged the kickdown switch, it was not working anyhow. unfortunately, no change, still stuck in 2nd.

I will try the vacuum related tests and report back with my findings.

wilburtual · #5 11-24-2013, 08:56 PM

I have tested the vacuum to the modulator with my Mityvac and it seems that is the issue... the plastic end cap piece on the modulator freely rotates around 360degrees.. at some positions it holds full vacuum, but when turned a little bit, it loses all vacuum.
When searching around the forum as well as looking at pelican parts for replacements, it seems most modulators are a type that has a black rubber cap on the end and the vac hose plugs into the body of the modulator. However, mine seems different. it has no rubber cap, instead a plastic cap piece on the end, that freely rotates around, and the vac hose plugs right onto the cap... anyone have any experience with this type of cap? I can't find any info on this type, or how to replace this cap- hopefully it is just the cap leaking and it can be swapped. I found a photo online of this sort of cap, I've attached for reference. But, I can't find anywhere that sells this type of replacement cap.. any ideas?

wilburtual · #6 11-24-2013, 09:26 PM

I just found this link to a replacement modulator... it seems this might be what my 81 240D has?

https:// m e r c e d e s s o u r c e .com/store/7221x-red-body-diesel-automatic-transmission-vacuum-modulator-instructions

ROLLGUY · #7 11-24-2013, 11:51 PM

Before buying a new modulator, try cleaning the cap and mounting surface, and replacing the Oring. I have had success with this, and have saved the expense of a modulator with a 25 cent Oring and some cleaning....Rich

cooljjay · #8 04-14-2014, 12:36 AM

The kick down solenoid can get stuck, mine did....it was bad....you can check it on the transmission by simply jumping the plug that goes into the switch....go under the car and touch the wire to the solenoid you should hear a click...no click its bad....it can also be removed and tested with the battery....positive line on the screw and negative on the bolt that goes into the transmission.

ROLLGUY · #9 04-14-2014, 12:54 AM

The modulator is available here on PP. It is around $70. It is located on the passenger side of the trans toward the rear of center (follow the vac line). The kickdown sol is on the forward part of the trans on the same side.

wilburtual · #10 04-14-2014, 01:50 AM

I can't seem to find the proper modulator part for this transmission. the only ones I see on PP are different styles, a black one and a green body one, whereas the one I have has a red body and a cream color swiveling cap - the vac line connects directly to the cap.
I am assuming they are not interchangeable.

I will jump the kickdown solenoid tomorrow to see if it clicks or not.

mdisav · #11 01-11-2015, 06:02 PM

Did you ever solve your issue?

wilburtual · #12 01-15-2015, 10:44 PM

I did not solve it unfortunately, I put in a brand new modulator and no change

I tried one more fluid drain and fill and there were pretty large shards of metal in the fluid.. so I am assuming something is toast inside the transmission.

But, swapping the modulator is easy if anyone ever needs to do it. and by fixing the vacuum leaks I did get 1st gear back, which i never had with this car.

With all the other issues the car had and parts it needed, and now a bum transmission... it has now moved on to the great junk yard in the sky. RIP Lucy, your brother Linus misses you :,(

pch2021 · #13 08-17-2018, 04:44 PM

you never checked vacuum supply to the modulator, did you? these forums are useless...

vwnate1 · #14 08-17-2018, 09:13 PM

No ;

Not useless, just not as good when the O.P. doesn't follow directions and never answers the questions given to help him figure out the actual problem .

I missed where he mentioned the tranny's model # when he was under the car repeatedly fooling with the modulator .

BTW : my '82 240D had a similar problem and fiddling with I don't remember what and adding Trans-X got it to shift again for several more years and close to 35,000 miles before the weeping ATF drove me bonkers .